Our long range goal is to understand biosynthesis, regulation and function of cytochrome c2 (cyt c2) in the electron transport chain of Rhodobacter sphaeroides. This periplasmic protein is a mobile electron carrier between distinct membrane bound redox complexes in both aerobic and photosynthetically grown cells. In particular we wish to determine how cyt c2 synthesis is accomplished and regulated relative to other redox carriers under defined physiological conditions which dictate cyt c2 function in electron transport. We will dissect the steps in cyt c2 biosynthesis relative to accumulation of cyt c2 in the periplasm. We will monitor in vivo expression of the cyt c2 structural gene (cycA) at the RNA and protein level to determine the physiological and molecular basis for the regulation of cyt c2 maturation and export by factors such as light, oxygen, and the presence of external electron acceptors. We will identify and characterize genetic regions controlling expression, maturation, and secretion of the cycA gene product. We will analyze the physiological effects of mutations in such genetic regions on synthesis of cyt c2 and, where appropriate, other components of the redox chain. Finally, we will study structure-function relationships in the cycA protein and determine the ability of specific mutant cyt c2 proteins to i) be assembled into functional redox carriers, ii) complement R. sphaeroides cyt c2-deficient mutants and iii) participate in electron transport reactions.